Pixel Driving Device, Light Emitting Device, and Property Parameter Acquisition Method in a Pixel Driving Device

1. A pixel driving device for driving a plurality of pixels, connected to each of a plurality of signal lines, and each comprising a light emitting element, and a pixel drive circuit having a drive transistor, which is for controlling current supplied to the light emitting element, and whose one end of a current path is connected to one terminal of the light emitting element, the pixel drive circuit further having a holding capacity for storing charge by voltage impressed on a control terminal of the drive transistor, the pixel driving device comprising: a voltage impressing circuit for outputting a reference voltage; a plurality of voltage measurement circuits equipped for connecting to each signal line; a switching circuit for switching connection of one end of each signal line, between the voltage impressing circuit and each voltage measurement circuit; and a property parameter acquisition circuit for acquiring property parameters that relate to electrical properties of each pixel; wherein the reference voltage has an electric potential in which an electric potential difference of the one end with respect to the other end of the current path of the drive transistor is a value that exceeds a threshold voltage of the drive transistor; wherein the switching circuit connects the one end of each signal line to the voltage impressing circuit and interrupts the connection between the one end of each signal line and the voltage impressing circuit after impressing the reference voltage for a predetermined time on the one end of each signal line by the voltage impressing circuit, and connects the one end of each signal line to each voltage measurement circuit after a predetermined settling time has elapsed; wherein each voltage measurement circuit acquires a voltage of the one end of each signal line as a measured voltage when connected with the one end of each signal line by the switching circuit; wherein the settling time is set to a value of a first settling time group and a value of a second settling time; wherein the first settling time group is constituted with a plurality of different time values, each of which is larger than a ratio (C/β0) where C is total capacity, which is, the sum of a parasitic capacity that is parasitic on a single signal line, a holding capacity, and a light emitting element capacity that is parasitic on the light emitting element, and β0 is a reference value of a current amplification factor; and the second settling time is constituted with a time value which is shorter than the ratio (C/β0); and wherein the property parameter acquisition circuit acquires the threshold voltage of the drive transistor for each pixel and the current amplification factor of the pixel drive circuit as a first property parameter in the property parameters based on voltage values of a plurality of measured voltages acquired by the plurality of voltage measurement circuits for the first settling time group; and the property parameter acquisition circuit acquires an irregularity parameter which indicates an irregularity of the current amplification factor as a second property parameter in the property parameters based on a value of the threshold voltage acquired for each pixel and values of measured voltages acquired by the voltage measurement circuits for the second settling time.

2. The pixel driving device according to claim 1 , wherein the reference value of the current amplification factor is a design value for the current amplification factor.

3. The pixel driving device according to claim 1 , wherein the first property parameter and the second property parameter are acquired during an initial state in which the drive transistor of each pixel has initial properties.

5. The pixel driving device according to claim 4 , wherein the property parameter acquisition circuit acquires the second property parameter, namely, a value of the irregularity parameter Δβ/β, based on equation (2) when the second settling time is t 3 , the deviation between pixels in a measured voltage for the second settling time is ΔVmeas(t 3 ), the voltage value of the reference voltage is Vref, the threshold voltage of each pixel is Vth, a mean value of a ratio of capacity content in the plurality of pixels to the current amplification factor is <C/β>, and the irregularity property is Δβ/β, Δ ⁢ ⁢ Vmeas ⁡ ( t ⁢ ⁢ 3 ) = - [ Δ ⁢ ⁢ β β ] × < C / β > t ⁢ ⁢ 3 ⁢ { 1 - 2 Vref - Vth ⁢ < C / β > t ⁢ ⁢ 3 } . ( 2 )

6. A light emitting device, comprising: a pixel array, which is constituted with a plurality of pixels, connected to each of a plurality of signal lines, and each comprising a light emitting element, and a pixel drive circuit having a drive transistor for controlling current supplied to the light emitting element with one end of a current path of the drive transistor connected to one terminal of the light emitting element, the pixel drive circuit further having a holding capacity for storing charge by voltage impressed on a current control terminal of the drive transistor; a voltage impressing circuit for outputting a reference voltage; a plurality of voltage measurement circuits equipped respectively for connecting to each of the plurality of signal lines; a switching circuit for switching connection of one end of each signal line, between the voltage impressing circuit and each voltage measurement circuit; and a property parameter acquisition circuit for acquiring property parameters that relate to electrical properties of each pixel; wherein the reference voltage has an electric potential in which an electric potential difference of the one end with respect to the other end of the current path of the drive transistor is a value that exceeds a threshold voltage of the drive transistor; wherein the switching circuit connects the one end of each signal line to the voltage impressing circuit and interrupts the connection between the one end of each signal line and the voltage impressing circuit after impressing the reference voltage for a predetermined time on the one end of each signal line by the voltage impressing circuit, and connects the one end of each signal line to each voltage measurement circuit after a predetermined settling time has elapsed; wherein each voltage measurement circuit acquires a voltage of the one end of each signal line as a measured voltage when being connected with the one end of each signal line by the switching circuit; wherein the settling time is set to respective values of a first settling time group and a second settling time; wherein the first settling time group is constituted with a plurality of different time values, each of which is larger than a ratio (C/β0) where C is total capacity, which is, the sum of a parasitic capacity that is parasitic on a single signal line, a holding capacity, and a light emitting element capacity that is parasitic on the light emitting element, and β0 is a reference value of a current amplification factor; and the second settling time is constituted with a time value which is shorter than the ratio (C/β0); and wherein the property parameter acquisition circuit acquires the threshold voltage of the drive transistor for each pixel and the current amplification factor of the pixel drive circuit as a first property parameter in the property parameters based on voltage values of a plurality of measured voltages acquired by the voltage measurement circuits for the first settling time group; and the property parameter acquisition circuit acquires an irregularity parameter that indicates an irregularity of the current amplification factor as a second property parameter in the property parameters based on a value of the threshold voltage acquired for each pixel and values of measured voltages acquired by the voltage measurement circuits for the second settling time.

7. The light emitting device according to claim 6 , wherein: the plurality of signal lines in the pixel array are respectively arranged along a first direction; the pixel array has at least one scan line arranged along a second direction orthogonal to the first direction; the plurality of pixels are arranged in the vicinity of each intersecting point of the scan line and the plurality of signal lines; the light emitting device further comprises a selection drive circuit for setting each pixel connected to the scan line to a selected state by impressing a selection signal on the scan line; and the property parameter acquisition circuit acquires the first property parameter for each pixel which is in the selected state by the selection drive circuit.

8. The light emitting device according to claim 7 , wherein the pixel drive circuit comprises: a first thin film transistor to which a predetermined power voltage is impressed on one end of a current path of the first thin film transistor, and which has a connection point connecting the other end of the current path of the first thin film transistor to the one terminal of the light emitting element; a second thin film transistor whose control terminal is connected to the scan line, one end of a current path is connected to the one end of the current path of the first thin film transistor, and the other end of the current path is connected to a control terminal of the first thin film transistor; and a third thin film transistor whose control terminal is connected to the scan line, one end of a current path is connected to a signal line, and the other end of the current path is connected to the connection point; wherein the first thin film transistor corresponds to the drive transistor, and when the pixel is in the selected state by the selection drive circuit, the second thin film transistor and the third thin film transistor enter an ON state, the one end of the current path of the first thin film transistor is connected with the control terminal of the first thin film transistor, and the signal line is connected to the connection point through the current path of the third thin film transistor whereby the reference voltage supplied from the voltage impressing circuit is impressed on the connection point through the third thin film transistor; and wherein each voltage measurement circuit acquires the voltage of the connection point of each pixel, arranged in the second direction and in the selected state, subsequent to each settling time elapsing, via the third thin film transistor and each signal line, as the measured voltages.

9. The light emitting device according to claim 6 , wherein the reference value of the current amplification factor is a design value for the current amplification factor.

10. The light emitting device according to claim 6 , wherein the acquisition of the first property parameter and the second property parameter in the property parameter acquisition circuit is executed during an initial state in which the drive transistor of each pixel has initial properties.

12. The light emitting device according to claim 6 , wherein the property parameter acquisition circuit acquires the second property parameter, namely, a value of the irregularity parameter Δβ/β based on equation (4) when the second settling time is t 3 , the deviation between pixels in a measured voltage for the second settling time is ΔVmeas(t 3 ), the voltage value of the reference voltage is Vref, the threshold voltage for each pixel is Vth, a mean value of a ratio of capacity content in the plurality of pixels to the current amplification factor is <C/β>, and the irregularity property is Δβ/β, Δ ⁢ ⁢ Vmeas ⁡ ( t ⁢ ⁢ 3 ) = - [ Δ ⁢ ⁢ β β ] × < C / β > t ⁢ ⁢ 3 ⁢ { 1 - 2 Vref - Vth ⁢ < C / β > t ⁢ ⁢ 3 } . ( 4 )

13. A property parameter acquisition method in a pixel driving device for driving a plurality of pixels, connected to each of a plurality of signal lines, and each comprising a light emitting element, and a pixel drive circuit having a drive transistor whose one end of a current path is connected to one terminal of the light emitting element for controlling current supplied to the light emitting element, the pixel drive circuit further having a holding capacity for storing charge determined by voltage impressed on a control terminal of the drive transistor, the method comprising: a reference voltage impressing step for connecting a voltage impressing circuit to one end of each signal line, and impressing a reference voltage on the one end of each signal line so that an electric potential difference of the one end to the other end of the current path of the drive transistor is a value that exceeds a threshold voltage of the drive transistor of the one end of each signal line; a measurement voltage acquisition step that interrupts the connection between the one end of each signal line and the voltage impressing circuit, and then acquires a voltage of the one end of each signal line as a measured voltage after passage of each of predetermined settling times after interrupting the connection; and a property parameter acquisition step for acquiring property parameters that relate to electrical properties of each pixel from the measured voltages; wherein the settling times in the measured voltage acquisition step are set to respective values of a first settling time group and a second settling time; wherein the first settling time group is constituted with a plurality of different time values, each of which is larger than a ratio (C/β0) where C is total capacity, which is, the sum of a parasitic capacity that is parasitic on a single signal line, a holding capacity, and a light emitting element capacity that is parasitic on the light emitting element, and β0 is a reference value of a current amplification factor, and the second settling time is constituted with a time value which is shorter than the ratio (C/β0); and wherein the property parameter acquisition step includes: a first property parameter acquisition step that acquires the threshold voltage of the drive transistor of each pixel and the current amplification factor of the pixel drive circuit as a first property parameter in the property parameters, based on values of measured voltages for the first settling time group; and a second property parameter acquisition step that acquires an irregularity parameter which indicates an irregularity of the current amplification factor as a second property parameter in the property parameters based on a value of the threshold voltage acquired for each pixel and values of measured voltages for the second settling time.

15. The property parameter acquisition method in the pixel driving device according to claim 13 , wherein the second property parameter acquisition step includes a step that acquires the second property parameter, namely, a value of the irregularity parameter Δβ/β for each pixel based on equation (6) when the second settling time is t 3 , the deviation between pixels in a measured voltage for the second settling time is Δmeas(t 3 ), the voltage value of the reference voltage is Vref, the threshold voltage for each pixel is Vth, a mean value of a ratio of capacity content in the plurality of pixels to the current amplification factor is <C/β>, and the irregularity property is Δβ/β, Δ ⁢ ⁢ Vmeas ⁡ ( t ⁢ ⁢ 3 ) = - [ Δ ⁢ ⁢ β β ] × < C / β > t ⁢ ⁢ 3 ⁢ { 1 - 2 Vref - Vth ⁢ < C / β > t ⁢ ⁢ 3 } . ( 6 )

16. A light emitting device, comprising: a plurality of pixels, connected to each of a plurality of signal lines, each comprising a light emitting element, and a drive transistor which has a current path and a control terminal, which connects one end of the current path to one terminal of the light emitting element, and which controls electric current supplied to the light emitting element through the current path based on voltage data written between the control terminal and the one end of the current path; a plurality of voltage measurement circuits for acquiring a voltage value as a measured voltage of one end of each signal line; and a property parameter acquisition circuit for acquiring property parameters that relate to electrical properties of each pixel; wherein each the voltage measurement circuit acquires the voltage value of the one end of each signal line, denoted as Vmeas(t) in equation (7), as a plurality of first measured voltages for a plurality of different settling times whose respective values satisfy the condition (C/β)/t<1 and as a second measured voltage, for a settling time whose value satisfies the condition (C/β)/t≧1, where the settling time is defined as the time elapsed from the time when an impressed voltage is stopped after the voltage is impressed on the one end of the current path of the drive transistor via the one end of each signal line so that an electric potential difference between the one end and the other end of the current path of the drive transistor exceeds a threshold voltage of the drive transistor, and then the one end of each signal line is set in a state of high impedance; and wherein the property parameter acquisition circuit acquires an irregularity parameter (Δβ/β) that indicates an irregularity of the voltage/current properties of the drive transistor of the plurality of pixels, as a property parameter, based on a plurality of first measured voltage values, and a value of the second measured voltage, acquired by each voltage measurement circuit, Vmeas ⁡ ( t ) = Vth + 1 t ( C / β ) + 1 Vref - Vth ( 7 ) where, t: settling time, Vmeas(t): the measured voltage acquired by each voltage measurement circuit at the elapsed settling time t, Vth: the threshold voltage of the drive transistor, Vref: Reference voltage, C: Total Capacity(C=Cs+Cp+Cel), Cs: Holding capacity, Cp: Wiring parasitic capacity, Cel: Light emitting element capacity, β: Current amplification factor of the pixel drive circuit.

17. The light emitting device according to claim 16 , wherein the property parameter acquisition circuit: acquires the Vth and the β, as the property parameters for the drive transistor, by substituting the plurality of first measured voltages acquired by each voltage measurement circuit for each pixel in equation (8) while the (C/β) value and an initial threshold voltage of the drive transistor are the property parameters; and acquires the irregularity parameter (Δβ/β) by substituting the acquired property parameters of the drive transistor, and the deviation ΔVmeas(t) at the plurality of pixels for the second measured voltage acquired by the voltage measurement circuit, in equation (9), Vmeas ⁡ ( t ) = Vth + ( C / β ) t ⁢ ⁢ ⁢ where , ( C / β ) < t ( 8 ) Δ ⁢ ⁢ Vmeas ⁡ ( t ) = - [ Δ ⁢ ⁢ β β ] × < C / β > t ⁢ { 1 - 2 Vref - Vth ⁢ < C / β > t } ( 9 ) where, ΔVmeas(t) is the deviation at the plurality of pixels for the measured voltage acquired by each voltage measurement circuit at the elapsed settling time t, and Δβ is the deviation of β at the plurality of pixels.